<!DOCTYPE html>
<html>

<head>
    <title> 事件</title>
    <script type="text/javascript">
    function count() {
        var x1 = parseInt(document.getElementById('txt1').value);
        var x2 = parseInt(document.getElementById('txt2').value);
        var y;
        var jsf = document.getElementById('select').value;
        alert(jsf);
        switch (jsf) {
            case '+':
                y = x1 + x2;
                break;
            case '-':
                y = x1 - x2;
                break;
            case '*':
                y = x1 * x2;
                break;
            case '/':
                y = x1 / x2;
        }
        document.getElementById('fruit').value = y;
        //获取第一个输入框的值
        //获取第二个输入框的值
        //获取选择框的值
        //获取通过下拉框来选择的值来改变加减乘除的运算法则
        //设置结果输入框的值

    }
    </script>
</head>

<body>
    <input type='text' id='txt1' />
    <select id='select'>
        <option value='+'>+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <input type='text' id='txt2' />
    <input type='button' value=' = ' onclick="count()" />
    <!--通过 = 按钮来调用创建的函数，得到结果-->
    <input type='text' id='fruit' />
</body>

</html>
